Laser rangefinders are becoming an increasingly vital component in high precision targeting engagements. The precise and accurate range to target information is an essential variable to the fire control equation of all future soldier weapons. This information is provided easily, and in a timely manner, by laser range finders.
Current fielded laser range finders are bulky, heavy and expensive. These laser range finders were not developed with the individual soldier and his special needs in mind.
The monoblock laser cavity (a laser subassembly, which lacks only an optical pump) described in U.S. Pat. No. 6,373,865, whose disclosure is hereby incorporated by reference, makes the development and fabrication of a very low cost, compact laser range finder feasible. The monoblock laser cavity incorporates all of the optical components required for a short-pulse laser on a thin substrate of the same or thermally equivalent material. These optical components are “locked” into alignment forming an optical laser cavity for flash lamp or diode laser pumping. The optical laser cavity never needs optical alignment after it is fabricated. The beam divergence of the monoblock laser is rather large (>8 mrad) (low brightness laser) which means a sizable optical system is required to collimate the monoblock laser output.
Referring to the drawings, FIG. 1 shows a conventional monoblock laser cavity 10. The monoblock laser cavity 10 is made up of a plurality of discrete optical elements which are disposed serially on a substrate 11 and which share a common optical axis 13. The typical cross-section is square or rectangular, even though it can take various other forms. The optical components are bonded into one “block,” hence the name “monoblock.” The optical elements include a laser rod 15 of gain material, a passive Q-switch 17, an optical parametric oscillator (OPO) 19, and an output coupler 21.
The laser rod 15 has a uniform slit 22 sliced through it at the Brewster angle to the optical axis 13, thus producing two polarizing rod elements 23 and 25 from the single rod of gain material. The high reflector (HR) 26 at the laser emission wavelength (e.g., 1064 nm) is coated on the input end face 27 of the laser rod 15.
A high reflector (HR) 28 at a laser emission wavelength (e.g., 1064 nm) and a partial reflector (PR) 29 at an OPO wavelength (e.g., 1570 nm) are coated on the output end face 30 of the output coupler 21. The HR coatings 26 and 28 act as the two mirrors defining an optical resonator.
The monoblock laser cavity 10 shown in FIG. 1 is a flat-flat or stable resonator design. This design is acutely sensitive to any angular deviations of the mirrors from the optical axis. It also allows high order modes of lasing to occur which leads to poor beam quality. Note that the conventional monoblock laser cavity is lengthened in an attempt to improve beam quality. The beam divergence from a flat-flat cavity is very weakly affected by cavity length.